The sudden rout of Valencia's army at Contreras on the morning of August 20 forced Santa Anna to resort to a second line of defense.  While the survivors of Valencia's army fled from Contreras toward Mexico City with General David Emanuel Twiggs' division in pursuit, Santa Anna stationed forces at fortifications prepared earlier along the Churubusco River, including some at the Convent of san Pablo.

In the foreground, the officers wear forage caps and frock coats, while others wear shell jackets; several artillerymen have striped trousers, which, combined with the view being fro the American perspective of the battle, suggests the lithographer based his work on an American sketch.  At right, a squadron of dragoons or mounted riflemen, wearing a mixture of forage caps and straw hats, gather behind some small huts for protection from Mexican cannon and musket fire.  At left, American infantry advances, again protected by small buildings while the foremost ranks deliver a volley.  In the middle distance, from left to right, a line of trees denotes the course of the Rio Churubusco, the banks of which served as a line of defense for the Mexican forces.  Smoke billows from the bustling fortifications of the convent, accurately depicted with its bell tower, buttresses, central dome and lantern, smaller two-story outbuildings, and an outer breastworks with prepared embrasures for cannon and infantry.  To the right and rear of the convent can be seen the tete du pont, or fortified bridgehead, that guarded the river crossing of the road from San Antonio to Mexico City.